Rubber products and the compositions used to produce them are a large economic factor in the world. There is a continuing search for compositions which will enhance the final product either by a cost savings or quality of the product.
The tendency for some vulcanized rubber products to "bloom" creates an undesirable appearance on the finished product. This "bloom" is believed to be a migration of some of the ingredients in the rubber to the surface and once there will form a light colored haze. The "bloom" is believed to be zinc salts and sulfur but also can comprise oils, antizonants, antioxidants and the like. An improvement in the appearance of the finished product could be obtained, if "bloom" could be lessened or eliminated.
"Bloom" in uncured rubber products has a serious effect on the ability of the rubber to stick to adjacent rubber. Many rubber products, such as tires, are plied one layer upon the other in the fabricating or uncured state. If one of these layers has a dry salt type dusting (bloom) on the surface, then the rubber's "tack" (that is, its tendency to want to latch onto the adjacent rubber) is severely reduced. Reduced bloom in the uncured rubber is very much needed.
Another major problem facing producers of rubber articles is the task of cleaning molds used to vulcanize rubber articles. These molds, which are usually metal, have a tendency to build up a scum or char over a period of time. Once the mold reaches a very dirty state, defects can appear in the cured article. Usually, the molds are cleaned when they become dirty enough to effect the product quality. Cleaning the molds is time consuming and results in production down-time. Means of keeping molds clean or better means of cleaning dirty molds are needed for the rubber industry.
Sponge rubber products are large volume rubber products and are used widely as weather stripping for automobiles. In making sponge products, it is customary to incorporate a gas-producing agent in the rubber composition. The composition is heated to a temperature sufficient to release the gas and vulcanize the rubber. Improved sponge rubber compositions are desirable.
As the price and availability of petroleum becomes a problem, there is a greater search for additives to rubber which are not based on oil or natural gas feedstocks. Materials which come from the soil have been an area of interest to rubber formulators. Materials such as clay, silica pigments, calcium carbonate and ground coal have become popular rubber fillers, due to their independence of the petroleum market.
U.S. Pat. No. 3,075,931 discloses rubber compositions having as a reinforcing filler, a partial polyvalent metal salt of coal derived humic acid. The humic acid was obtained by the controlled burning of coal. The humic acids prepared by the controlled oxidation of coal have molecular weights of about 700 to 1400. The humic acid was added to the rubber latex in the form of an aqueous sodium humate solution and then the latex was coagulated using an acid salt such as calcium chloride.
U.S. Pat. No. 3,356,623 teaches using a water soluble salt of humic acid as a dispersing agent in a latex of rubber, precipitating the dispersing agent in situ by adding a water soluble zinc compound and an acid such as hydrochloric acid. The vulcanizing agents and all other compounding ingredients are added to the latex such that the precipitate is a completely formulated, vulcanizable rubber stock.
U.S. Pat. No. 3,533,988 discloses preparing a rubber masterbatch containing a salt of humic acid with a water soluble volatile base such as ammonia or a volatile amine. The humic acid used came from the oxidation of coal and had a molecular weight of from 700 to 1400. The rubber-humic acid masterbatch was dried at about 300.degree. F. (149.degree. C.) to drive off the ammonia. The dried masterbatch was mixed with other compounding ingredients and vulcanized.
Humic acid materials that must be manufactured from the burning of coal are hard, black, brittle solids with relatively low molecular weights (700-1400), and such materials are not suitable for use in our invention.
The elastomer forming industry, and particularly the rubber industry, is constantly searching for more effective and economical fillers which will not adversely affect the properties of shaped articles formed from the rubber compositions used. The humate used in our composition provides such a filler.